In the course, we introduced various mechanisms for reliable data transfer.

$$ Checksum

$$ ACK $($confirmation message$)$

$$ Timer

$$ Sequence numbering

A sender and receiver are connected to each other via two one$-$way communication channels. G$-$A $($g sender $->$

receiver$)$ channel may corrupt or lose packets passing through it$,$ while the A$-$G $($receiver $->$ sender$)$

The channel is perfect $($no packet corruption or loss$).$ The delay in both channels is within a certain level.

is always less than its value. The order of the packets in the channels is not disrupted $($in$-$order trans$-$

mission$).$ In accordance with this given scenario, the relationship between the sender and the receiver is reliable.

Design a data transfer protocol. The protocol requires all of the above $4$ mechanisms.

Use the ones. Your solution doesn't have to be efficient; It just needs to work correctly.

$($a$)$ Draw the finite state machines $($FSM$)$ for the sender and receiver.

$($b$)$ Among the above $4$ mechanisms, the roles $($purposes$)$ of the ones you use in the protocol.

and explain why a reliable protocol cannot exist without them.